Understanding Hydrological Sensitivities Induced by Various Forcing Agents with a Climate Model

The apparent hydrological sensitivity, defined as the global- mean precipitation change per increase of the global-mean tem- perature, is investigated for scenarios induced by different forcing agents. Simulations with a climate model driven individually by four different climate forcers, i.e. sulfate, black carbon, solar insolation and carbon dioxide (CO2), are analyzed in the context of energy balance controls on global precipitation to explore how different forcing agents perturb different energy components grouped into fast and slow responses. Similarities and differences among the forcing agents are found in ingredients of the tendency contributing to the hydrological sensitivity from various energy budget components. Specifically, the sulfate and solar forcings induce the hydrological sensitivity of ~2.5%K−1 due to the slow response of radiative cooling whereas the black carbon induces a significantly negative hydrological sensitivity (~ −6.0%K−1) due to the strong atmospheric heating. The CO2-induced hydrological sensitivity is found in between (~1.2%K−1) as a result from the slow response of radiative cooling and its partial compensation by the atmospheric heating. The findings provide a quantitative basis for interpreting climatic changes of global precipitation driven by a mixture of various natural and anthropogenic forcings.